Microwave identification of railroad cars



April 19, 19 6 o. F. HAMANN ETAL 3,247,514;

MICROWAVE IDENTIFICATION OF RAILROAD CARS Original Filed Oct. 4, 1963 3Sheets-Sheet 2 INVENTORS OMER F. HAMANN SHERMAN H. BOYD M6 W i April1965 o. F. HAMANN ETAL 3,247,514

MICROWAVE IDENTIFICATION OF RAILROAD CARS Original Filed Oct. 4, 1963 3Sheets-Sheet 5 INVENTORS OMER F. HAMANN SHERMAN H. BOYD United StatesPatent 3,247,514 WCROWAVE IDENTIFICATION or RAILROAD CARS Omer F.Hamann, La Joila, and Sherman H. Boyd, San

Diego, Calif., assignors to American Brake Shoe Company, New York, N.Y.,a corporation of Delaware Original application Oct. 4, 1963, Ser. No.319,914. Divided and this application Oct. 5, 1965, Ser. No.

Claims. (Cl. 343-18) This application is a division of co-pendingapplication Serial No. 319,914, filed October 4, 1963, which in turn isa continuation-in-part of application Serial No. 160,004, filed December18, 1961, and now abandoned.

This invention relates to new and improved identification members foruse in a system for identifying railway cars and other large objects,and more particularly in an improved automatic all-weather microwave caridentification system.

It is critically important for railroad management to know, at alltimes, the locations of the locomotives and cars belonging to a railroadsystem. If a car is loaded, information as to its location enables therailroad to answer questions from the shipper or shippers; if the car isempty, information as to its location is essential to enable the car tobe put into use when needed. Because both locomotives and cars requireperiodic service, information as to their location is also important forthis purpose.

Maintenance of a running record of the location of the cars,locomotives, and other like equipment is made difficult because theindividual cars may be diverted to any of a plurality of locations andmay remain there for long periods of time. By the same token, a carshunted to an isolated siding may remain there for an indefinite periodif no adequate record of its location is maintained. In most instances,records of car locations have been maintained primarily by hand-writtenmemoranda prepared by checks in the larger yards and by other personnelin small yards and at individual sidings. As might be expected, thiskind of reporting is subject to human error and is also subject to asubstantial time lag insofar as preparation and forwarding of records isconcerned.

The need to mechanize the reporting and recording of car and locomotivelocation information has been recognized, in the railroad industry andin other similar fields for some time. A number of suggestions that havebeen advanced with respect to automatic identification systems haveproved impractical because they require .overly complex and expensiveequipment on the cars themselves. Other systems, although attractivefrom an economic standpoint, have not proved desirable because they arenot effectively operable under adverse environmental conditions such asrain, fog, or storms. "Indeed, many systems relying upon visualrecognition of car numbers and other identifying data painted on thecars themselves have been diificult to keep in operation because thesymbols tend to be obscured by dirt on the cars. Moreover, many suchsystems still require manual entries and reports and thus do notaccomplish complete automation of the car identification procedure.

There are distinct economic limitations with respect to any systemadopted with respect to automatic identification of railroad cars andother vehicles. One problem presented in connection with such systemshas to do with the large number of cars. Thus, any car identificationsystem requiring the mounting of any equipment of substantial complexityon the individual cars is quite impractical from an economic standpoint.From a purely economic point of view, the cost of the individualidentification elements on the cars must be kept below 3,247,514Patented Apr. 19, 1966 ten dollars and preferably should be less thanfive dollars. Accordingly, the use of active circuit elements such asamplifiers and transmitters, or storage devices such as magnetic cores,magnetic tape, or the like, on the railroad cars, is out of the questionbecause of excessive cost. Optical systems with painted marks on thecars, as noted above, are objectionable because they are not reliableduring rain, snow, fog, or excessive dust conditions. The sameconsiderations, in whole or in part, apply to other objectidentification applications; e.g., automobiles, trucks and. likevehicles.

The principal object of the present invention, therefore, is to providenovel coded identification members, suitable for use in automaticrailroad car and other object identification systems, that effectivelyovercome the diificulties and disadvantages of previously knownapparatus.

Another important object of the present invention is to provide, in anautomatic railway car or like object identification system,identification devices, mounted on the cars, consisting solely ofpassive elements that can be readily and inexpensively mass produced.

A particular object of the invention is to provide new and improvedpassive code elements capable of modifying and reflecting a receivedmicrowave or other radiant energy signal in a manner affording areliably high signal-to-noise level at a receiver positioned to pick upthe reflected signals.

Another object of the invention is the utilization of a shift inpolarization as a basis for distinguishing the reflected code signalsfrom the original signal and from stray reflections. An importantfeature of the invention, in this regard, is the employment of resonantreflector elements as the coded identification devices.

Accordingly, the present invention relates to a coded identificationmember for use in an automatic object identifying system, such as avehicle identifying system, of the kind comprising a scanning stationincluding a source of radiant energy signals of given wavelength,radiating means for radiating said signals with a first predeterminedpolarization, and receiving means for receiving signals of thatwavelength but limited to reception of signals of a second andsubstantially different polarization. The identification membercomprises a plurality of individual reflector elements arranged in apredetermined code sequence, each effective to reflect impinging signalsof the aforesaid wavelength but with said second polarization. Theidentification member further comprises means for mounting the reflectorelements on an object to be identified in position to intercept andre-radiate the signals from the radiating means back to the receivingmeans when that object is in predetermined position relative to thescanning station.

Other and further objects of the present invention will be apparent fromthe following description and claims and are illustrated in theaccompanying drawings which, by way of illustration, show preferredembodiments of the present invention and the principles thereof and whatis now considered to be the best mode contemplated for applying theseprinciples. Other embodiments of the invention embodying the same orequivalent principles may be made as desired by those skilled in the artwithout departing from the present invention and the purview of theappended claims.

In the drawings:

FIG. 1 is a block diagram of a railway car identifying system in whichthe present invention may be employed;

FIG. 1A is a partially schematic perspective view of a tracksidescanning station for the system of FIG. 1, showing the operationalrelationship of the scanning station to the railway cars beingidentified;

FIG. 2 is a perspective view of one embodiment of a coded reflectormember, constructed in accordance with one embodiment of the presentinvention, used in the system of FIG. 1;

FIG. 3 is a perspective View of another embodiment of the codedreflector member of the invention;

FIG. 4 is a perspective view of a plurality of reflector membersassembled to form a coded object identification member;

FIG. 5 is a perspective view of yet another embodiment of the codedreflector member of the invention; and

FIG. 6 is a perspective view of a further embodiment of coded reflectormembers constructed in accordance with the present invention.

FIGS. 1 and 1A illustrate an automatic railway car identifying system10. The system it) includes a first trackside scanning station 11 and asecond and similar trackside scanning station 11A. At station 11, asshown in FIGS. 1 and 1A, there is located a transmitting antenna 16,connected to a scanner transmitter 17, and a receiving antenna 18 thatis connected to a scanner receiver 19.

A train 13 moving past the scanning station 11 (FIG. 1A) brings eachindividual car 12 into scanning position opposite the scanning station.Each car 12 carries an identification member or plate 14, comprising aplurality of coded reflector members, attached to the car at a suit ablelocation coinciding approximately with the common focus of the twoantennas 16 and 18. One suitable location for the identification plates14, on the railway cars 12, is on the wheel carriage immediately abovethe springs, since this location is relatively well standardized withrespect to height above the railway track. On those relatively few carswhere this particular location cannot be used, as on cars on which it ismasked by some downwardly projecting exterior element of the car, adifferent mounting arrangement may be employed, so long as theidentification members on the cars are located at approximately constantheights relative to the antennas. The location of the identificationmembers 14 lengthwise of the cars 12 is not critical; either truck maybe selected or the plates may be mounted at the mid-points of the cars.Preferably, there are two plates 14 for each car, one on each side, sothat it is not necessary to duplicate the scanning station 11 on theopposite side of the railway track.

The scanning station 11A constitutes, essentially, a duplicate ofstation 11. Thus, it includes a scanner transmitter 17A connected to aradiating antenna 16A (FIG. 1). The scanning station also includes areceiving antenna 18A that is connected to a scanner receiver 19A. Inactual practice, in the system as illustrated, each of the receivingantennas 18 constitutes a dual antenna structure capable ofdiscriminating between received signals of two distinct polarizations.

In the operation of the car identification system 10, the selection ofoperating frequency is of substantial importance. Optimum results areobtained when the scanning signals employed at the scanning stations,such as stations 11 and 11A, are in the microwave range of five to fortykilomegacycles. That is, the scanning signals should be in a frequencyrange having wavelengths between 0.75 and 6.0 centimeters. Thisparticular operating range of microwave signal frequencies produces thedesired resolution for code signals reflected by the coded reflectormembers of the identification members 14, which are described in detailhereinafter. The identification plates 14 may be held to a reasonablesize when utilizing signals in this particular range. Further, themicrowave signals within the stated range may be convenientlytransmitted by available equipment tested and proven by substantialcommercial use.

One form of coded reflector member that may be utilized in theconstruction of one of the identification members 14 is illustrated inFIG. 2. The coded reflector member 20 comprises a sheet of conductivematerial, such as a thin aluminum sheet, having a fairly smooth surfaceand having a plurality of slots, 22, 24, 26 and 28 formed therein. Theseslots are each equal in length to one-half the wavelength of themicrowave signal radiated by antenna 1.6. Thus, said slot constitutes adipole reflector element resonant at the operating frequency of thesystem. The slots 22, 24, 26, 28 may be grouped according toorientation, orientation of the slots being critical in operation of thesystem as described more fully hereinafter. In the illustratedarrangement, the slots 24 and 26 represent code zeros and are orientedat 45 to the vertical. The slots 22 and 28, on the other hand,constitute code ones and are each oriented at an angle of +45 to thevertical. It is thus seen that the code for the reflector member 20, inbinary notation, is 1001, and is equivalent to the decimal numeral nine.

In system 10, the microwave scanning signal from the transmitter antenna16 at station 11 (FIG. 1) is radiated with a vertical polarization,upwardly directed, as indicated by arrow '71. This signal, impingingupon one of the one slots 22 or 28 of the reflector element 20 (FIG. 2)is reflected and re-radiated with a different polarization, in thisinstance at an angle of .+45 relative to the original verticalpolarization.

On the other hand, the same microwave signal impinging upon the portionof the conductive reflector 2% including the dipole 24 or the dipole 26is reflected and re-radiated with a polarization rotation of 45 to thevertical. Thus, the signal from antenna 16 is reflected toward the dualreceiving antenna 18 with a rotation of polarization of either plus orminus 45 as shown by the arrows 72 and 73 in FIG. 1. The dual antenna 13includes two receiving wave guides for distinguishing between receivedsignals that are horizontally polarized in directions thus displaced byIt is thus seen that the angled dipole slots 22-23 act as selectivere-radiators and constitute effective code elements for theidentification system.

Utilizing microwave signals in the range of wavelengths from 0.75 to 6.0centimeters, the dipole slots 22, 24, 26, 28 should have a length of0.375 to 3.0 centimeters, depending upon the particular frequencyselected for microwave scanning. The width of each dipole should be lessthan one-quarter of the operating wavelength and preferably should beabout one-tenth of that Wavelength. Furthermore, the dipoles should bespaced from each other by a distance of one full wavelength or more.These dimensions permit each reflector member 25 to be quite small; moreparticularly, the individual reflector member, carrying either four orfive dipole reflector elements, may be of the order of two inches inheight and less than four inches in length.

It will be recognized that more than one of the reflector members 249 isrequired to aflord complete identification of a given railway car orlike vehicle. In a typical arrangement, the railroad owning the car andthe specific car itself may be identified by a code combinationcomprising, for example, three letters and six decimal numerals. Theletters can each be fully represented by one reflector member containinga total of five dipole reflector elements such as the slots 22-28, sincea five-digit code gives full identification of the letters of thealphabet with additional code symbols to spare. As many as six numericalcode elements may be required to identify the individual cars of a givenrailroad and these can be encompassed, for each numeral, by a reflectormember including four individual dipoles. Thus, with reflector membersof less than four inches in length, it is seen that the complete caridentification data may be assembled in an identification plate having atotal length of less than thirty-six inches.

In the car identification system 1%, each of the scanning stations suchas stations 11 and 11A may include a complete microwave signal generatorwith a local power supply. In a relatively compact yard, on the otherhand,

, antenna 18 by each car.

,5 the cost of identification system installation may be reduced, in atleast some instances, by utilizing a single microwave signal generatorcoupled to two or more of the trackside scanning stations. Anarrangement of this kind is illustrated in FIGS. 1 and 1A, with a singlemicrowave signal generator 21 coupled to the two scanner transmitters 17and 17A to provide those transmitters with the necessary microwavesignal for radiation. With this arrangement, the transmitters at thescanning stations need be nothing more complex or expensive thanrelatively simple amplifiers.

Using a single centralized microwave Signal generator, as shown in theblock diagram of FIG. 1, a number of diflerent methods may be employedto couple the signal generator to the various scanning stations of thesystem.

' For example, and as shown in FIG. 1A, the microwave signal may besupplied to the transmitters through a conductive link 36. On the otherhand, the microwave information may be transmitted to and from thecentral station of the system by means of a suitable radiation link asexemplified by the antennas 34. The illustrated ar rangement, utilizinga single signal generator for several scanning stations, has theadvantage that only passive transmission elements or simple amplifiersare required in the field, facilitating maintenance and servicing of themicrowave equipment. On the other hand, it is quite possible andpractical to locate individual microwave sig- 1 nal generators at thetrackside scanning station and this arrangement may well be adopted.

As shown in FIG. 1, each of the scanner receivers 19,

- 19A, at the scanning stations are coupled to a control unit from thetrackside scanning stations to the centralized control unit may be bymeans of a wire circuit or by a radiation link.

The control unit 29 is coupled to a butter storage register 31 which, inturn, may be connected to a tape punch 33. The binary coding or othercode employed for the car identification system may correspond directlyto the code required for operation of a conventional tape punch unit.Alternatively, the storage register 31 may include code translationapparatus to translate the received signals into a code compatible withthe tape punch. The tape from punch 33 may be fed to a tape reader 37connected back to the control unit 29. A data processing apparatus ordisplay unit 39 is connected to the control unit and is utilized toperform any desired computations withrespect to the car identificationdata made available 3 by the system and to display such data whenrequired.

In operation of the system shown in FIGS. 1 and 1A, a microwave signalof selected frequency is supplied by signal generator 21 to the scanningtransmitter circuit 17 at the trackside scanning station 11. This signalis applied to transmitting antenna 16 and preferably is radiatedcontinuously by that antenna. In any event, tb' microwave signal isbroadcast at all times when it is desired to identify rolling stockmoving past the scanning station. As noted above, the radiated signal isvertically I polarized.

When a car, locomotive, or other railway vehicle passes through thescanning station 11, the radiated microwave energy from antenna 16 isreflected back to the receiving Inevitably, there is a substantialamount of stray reflected radiation. The stray reflected radiation fromthe trucks and other parts of the cars does not produce signals ofsubstantial amplitude 'in the electrical receiving circuits connected tothe receiving antenna 18 because such stray reflected signals retain,for the most part, the vertical polarization employed for the radiatedsignals, whereas the receiving antenna structures of the device 18 aresensitive only to radiations polarized at plus or minus 45 to thevertical, and afford a high rejection of vertically polarized signals.

When the microwave beam impinges upon one of the dipole slots of a codedreflector element such as the element 200i FIG. 2, however, thereceivedradiation is reflected in substantial amplitude and with rotation of 45,plus or minus, depending upon the dipole orientation. Because thedipoles are resonant at the operating frequency of the system, theamplitude of the reflected and re-radiated signals is substantiallygreater than the amplitude of stray reflections, materially assisting inthe necessary maintenance of distinction between the reflected codesignals and stray reflections. Furthermore, the polarization rotationeflected by the resonant dipoles produces a substantially horizontalcomponent in the reflected and re-radiated signals. As a result, thesesignals impinging upon the dual antenna 18 produce electrical signals ofsubstantial amplitude in the operating circuits of scanner receiver 19(FIG. 1) and these signal impulses impart the necessary identificationinformation with respect to the car or other vehicle traversing thescanning station.

The digital signal pulses derived at the scanner receiver 19 are appliedto the control unit 29. These signal pulses do not recur at a ratesatisfactory for direct processing or read-out, using presentlyavailable equipment such as the tape punch 33. Moreover, the pulse ratemay vary by as much as 12: 1, since the train may move through thescanning station at speeds from five to sixty miles per hour. For thisreason, it is desirable to store the data temporarily. This isaccomplished by applying the received digital signals to the bufferstorage register 31, which may comprise one or more conventionaltransistor or magnetic core shift registers.

From the buffer storage register 31, the recorded information is readout to the tape punch 33 and is employed to control punching of a tape41, thereby affording a permanent record of the car identification. Inthe course of the same read-out of data from register 31, theidentification data may be transmitted to a remote location forprocessing, display, or other use. On the other hand, and particularlyif any end use for the information is to take place at the same locationas the operating equipment illustrated in FIG. 1, the tape 41 maysubsequently be passed through the tape reader 37, with the output fromthe tape reader being applied through control unit 29 to a suitable dataprocessor or display unit 39. The output from reader 37 may be transmitted to other locations aswell as'to processor 39. The device 39 mayprepare printed records of the cars in a given train or may be employedfor other like purposes pertinent to operation of the railroad.

The direction of movement of a given car through the scanning station isnot known in advance. Consequently, the system 10 provides foridentification of each car, from the data carried by the identificationplates 14 on the car, regardless of the direction in which the carmoves. This is accomplished by adding a coded reflector member at eachend of the identification plate 14, one of these additional codedreflector members being provided with a unique code to indicate movementof the car in one direction and the other being encoded with a differentunique code to indicate movement in the opposite direction. For example,the end reflector member for the plate 14 may be encoded with the binarycode 10101 to indicate that the car is moving in one direction, whenthis code is read first in the scanning of the identification plate. Theopposite end reflector member of the identification plate can beencoded, for example, as 01010 to indicate that the car is moving in theopposite direction. With such additional code data on the identificationplates, it is a relatively simple matter to provide the control unit 29with suitable circuits for identifying which code symbol has firstappeared in the digital signal derived by scanning of a given car and tocontrol the readout from buffer 7 store 31 to tape punch 33 to place thecode characters in the proper sequence on the punch tape 41. v

The coded reflector member 20, with the slot dipoles 22, 24, 26 and 23,is of substantial advantage in distingu'ishing the code signal pulsefrom extraneous reflections of the microwave signals as they impingeupon other parts of the railroad cars 12. The slot dipoles, however,also re-radiate the microwave signals in a direction away from thescanning station as well as toward the scanning station. Under someconditions, the backwardly-directed radiations from one slot may excitean adjacent slot dipole and produce a fairly strong spurious signal.This effect is minimized by the construction for the coded reflectormember 20 illustrated in FIG. 3.

Thus, to minimize the backward radiation from the dipole antennas, thereflector member 20 is provided with a backing 31 of a material thatabsorbs microwave frequency radiations. A number of such absorbentmaterials are known and are commercially available. This constructionobviates errors that might otherwise arise from spurious signals causedby transmission of the radiations from one slot to another.

in the modified construction shown in FIG. 3, it should also be notedthat the individual reflector members containing the slot dipoles arenot combined in a single physically unified plate but rather areconstructed as separate individual dipole plates or reflector elements33 assembled together to form the reflector member 2t). Thisconstruction has the advantage that no more than two different forms ofdipole plate are required, whereas the construction shown in FIG. 2entails the manufacture of a distinctively different reflector memberfor each ditferent character to be encoded in the identification system.

The arrangement of FIG. 3 is more economical from the standpoint ofreduction in the stock of parts required to assemble new identificationplates and the number of different kinds of reflector members that mustbe manufactured. However, use of physically separate reflector elements33, as shown in FIG. 3, requires greater knowledge on the part of theperson assembling the identification plates 14, since that person mustbe fully cognizant of the binary code employed in order to prepare thecorrect sequence of dipoles for each character. The arrangement of FIG.2, with the alpha-numeric symbol on the composite reflector membercontaining several reflector elements, allows somewhat more effectiveassembly and checking of identification plates by unskilled personnel.

In those instances where the radiation-absorbent material 31 is aflflxedto each individual reflector element 33, front-to-back reversal of theelements is impractical because the absorbent material would thus faceoutwardly of the assembly. This difliculty can be eliminated by usingreflector elements 33 of square configuration. The reflector element canthen be re-positioned by rotation through an angle of 90 to reverse theorientation of the dipole slot. This retains the position of theabsorbent material at the back of the dipole, and permits assembly ofany desired code combination using only a single form of reflectorelement.

FIG. 4 illustrates one manner in which the code reflector members may beassembled to form the identification plate 14. Thus, the identificationplate may include a suitable frame member 32 attached to the wheelcarriage or other suitable location on the railroad car. The codedreflector members 20, with or without a radiationabsorbent backing, areinserted in the frame to assemble the complete identification plate. Ofcourse, an analogous arrangement can be used with the individualreflector elements 33 (FIG. 3), assembling the code character reflectormembers directly in frame member 32.

FIG. 5 illustrates another form of coded reflector member that may beemployed in the system of the present invention. The reflector membershown in this figure comprises a sheet of radiation-absorbent materialitl, one face of which initially carries a thin continuous sheet ofconductive material. The conductive material is selectively etched orotherwise cut away to afford a series of strips or strands 42, 44 ofone-half wave length and of the desired orientation. Thus, the strips orstrands 42 and 44 constitute the individual reflector elements in thisform of the reflector member. The conductive strips, like the dipolesdiscussed hereinabove, are made resonant at the operating frequency ofthe scanning system. Thus, they reflect the impinging verticallypolarized microwave signals with a 45 rotation of polarization, thedirection of rotation being dependent upon the orientation of thestrips. Stray reflections are reduced by the absorbent material 4dappearing between and behind the resonant reflectors. Of course,individual wire elements mounted on the backing 45) can be employed inthe same manner as conductive strips 42, 44.

Another embodiment of the coded reflector member construction isillustrated in FIG. '6. Here, the coded reflector members 46 and dfleachcomprise a conductive structure having a base plate 56 and a pluralityof extending parallel plates 52 and 54, respectively. The depth of theslots between the plates 52 and 54 is selected to provide a time delayof one-quarter wavelength between the signal reflected from the frontedge of the plate and the signal reflected from the base member.Vertically polarized microwave signals impinging upon the members 46 and48 are reflected as right and left-hand circularly polarized signalsrespectively, which can be clearly distinguished by appropriate antennastructures incorporated in the dual receiving antenna 18.

If desired, the coded reflector members may be provided with aprotective coating of a material that is essentially transparent tomicrowave radiation. For example, a layer of polytetrafluoroethylene orother suitable plastic may be applied to the surfaces of the reflectormembers to protect them against adverse weather conditions. Thepolytetrafluoroethylene plastic and similar materials are of particularadvantage because they afford a surface which tends to rejectcontamination due to rain, snow, dust and the like, due to theiressentially non-adhesive properties. Thus, attenuation or scattering dueto the presence of surface contamination may be minimized.

In some instances, it may be desirable to modify the system to show thetype of car passing through the scanning station, determining whether itis a box car, a refrigerator car, a locomotive, a gondola, or other caror vehicle. This information can be incorporated in the coded datapresented by the identification plate 14 affixed to the car. Indeed, theidentification plate may be encoded to represent the data on which thecar requires servicing, the type of cargo contained by the car, andother such information. Thus, computing equipment at the central oflicecan be provided with information enabling it to list all cars due forservicing as of a given time, or can list all cars carrying a particulartype of cargo, or all cars constituting unloaded refrigeration cars. Ofcourse, a balance must be maintained between the amount of informationincorporated in the identification plates and the length required forsuch plates in order to avoid an eX-cessive burden on the system in theform of undue extension of the identification plate length.

In the foregoing description, the individual reflector elements havebeen shown oriented at angles of plus and minus 45 to the vertical todistinguish code zeros from code ones. It will be recognized, however,that other angles may be employed for this purpose. It is preferable,however, that the slots be perpendicular to each other to aiford maximumdistinction at the receiving antenna 18 and the receiver circuits 19.That is, orientation of the slots perpendicular to each other permitsthe most precise discrimination between the re-radiated signals from thedual angled dipoles.

It is even possible to use horizontally and vertically orientedreflector dipoles as the reflector elements in the system. Theseparticular orientations are not especially desirable, however.Horizontal movement of the train can introduce distortion into thereflected signals sutficient to degrade the signals-to-noise ratio andhence may prevent adequate discrimination between the re-radiatedsignals. Furthermore, the spaces between adjacent reflector members orindividual reflector elements in the identification plates 14 mayfunction as vertical slot antennas, reradiating the impinging signals ina manner such as to introduce spurious pulse signals at the receivingantenna.

While linear coding reflector elements are preferable these elements maycomprise other geometrical figures such as ellipses, ovals, and thelike. Alternatively, the reflector elements may be in the form ofhelices, spirals, or any other shapes which, in addition to theembodiment of FIG. 6, will produce circularly or elliptically polarizedsignals. Resonant reflector elements producing, for example, rightandleft-circularly polarized signals to represent binary ones and zeros,respectively, may give added improvement in the signal-to-noise ratio.

As will be evident from the foregoing description, the identificationapparatus of the present invention affords a number of distinctadvantages over previously known systems. The coded reflector membersthat make up the identification plates are simple and inexpensive tomanufacture and may be readily mass produced. The identification platesto be mounted on the rolling stock constitute passive code elements anddo not require amplifiers, power supplies, or like devices. As aconsequence, virtually no maintenance is necessary with respect to theidentification members on the cars. The equipment at the scanningstations is simple and inexpensive and requires a minimum ofmaintenance. Finally, car identity information is immediately availableat a central ofiice, where it may be used to up-date a running inventoryof the railroad stock or for any other required pu-npose.

Hence, while preferred embodiments of the invention have been describedand illustrated, it is to he understood that they are capable ofvariation and modification, and we therefore do not wish to be limitedto the precise details set forth, but desire to avail ourselves of suchchanges and alterations as fall within the purview of the followingclaims.

We claim:

1. A coded identification member for use in an automatic objectidentifying system comprising a scanning station including a source ofradiant energy signals of given wavelength, radiating means forradiating said signals with a first predetermined polarization, andreceiving means for receiving radiant energy signals of said givenwavelength but limited to reception of signals having a second andsubstantially different polarization, said identification membercomprising:

a plurality of individual reflector elements arranged in a predeterminedcode sequence, each effective to reflect impinging radiant energysignals of said given wavelength but with said second polarization;

and means for mounting said reflector elements on an object to beidentified in position to intercept and re-radiate said radiant energysignals from said radiating means back to said receiving means when saidobject is in predetermined position relative to said scanning station.

2. A coded identification member according to claim 1 for use in anobject identifying system in which said signal source is a microwavesignal generator and in which said transmitting and receiving means eachcomprise a microwave antenna, said reflector elements each comprising anelectrically conductive element dimensioned to reflect microwave signalsof said given wavelength and oriented to change the polarization of thereflected signal to said second polarization.

3. An identification member according to claim 2 in which each of saidreflector elements comprises a conduci0 tive metal sheet having a dipoleslot therein that is onehalf wavelength in length and less thanone-quarter wavelength in width.

4. An identification member according to claim 2 in which each of saidreflector elements comprises a radiation-absorptive backing supporting aconductive dipole structure.

5. An identification member according to claim 1 in which said reflectorelements are grouped in distinct code groups each representative of agiven alpha-numeric character, and in which each such group isconstructed as a unitary reflector member.

6. An identification member according to claim 1 in which individualones of said reflector elements are disposed perpendicular to each otherto distinguish between differing code values.

7. A coded identification member for use in an automatic objectidentifying system comprising a scanning station including a source ofradiant energy signals at a given frequency, transmitter means coupledto said signal source for radiating said signal with a given initialpolarization, and receiver means sensitive to a second and substantiallydifferent polarization, said identification member comprising:

a plurality of individual reflector elements;

and means for mounting said reflector elements on an object to beidentified in a predetermined code sequence, in position to interceptand re-radiate said radiant energy signals from said transmitter meansback to said receiver means with a substantial change in polarization.to said second polarization.

8. A coded identification member for an automatic vehicle identificationsystem employing short-range microwave scanning of individual vehicleidentification members, comprising:

a plurality of individual reflector dipoles, resonant at a givenmicrowave frequency, arranged in a predetermined alignment and spacingsequence in accordance with a given binary code to afford a unique codeidentification for a vehicle.

9. A coded identification member for an automatic vehicle identificationsystem employing short-range microwave scanning of individual vehicleidentification members, comprising:

a plurality of individual linear reflector dipoles, each having a lengthof one-half Wavelength and a width less than one-quarter wavelength at agiven microwave frequency, arranged in a predetermined alignment andspacing sequence in accordance with a given binary code to afford aunique code identification for a vehicle.

10. A coded identification member for an automatic object identificationsystem employing short-range microwave scanning of individual objectidentification members, comprising:

a plurality of individual reflector elements each including a conductivebase plate and a plurality of parallel conductive elements projectingtherefrom through a distance of approximately one-fourth Wavelength;

and means for mounting said reflector elements in a predeterminedalignment and spacing sequence, according .to a given binary code, toafford a unique code identification for an object constitutingcircularly polarized microwave radiations.

References Cited by the Examiner Microwaves Identify Freight Cars, by O.F. Hamann et al., Control Engineering, vol. 9, No. 3, March 1962, pages102-104 relied upon.

CHESTER L. JUSTUS, Primary Examiner.

P. M. HINDERSTEIN, Assistant Examiner.

1. A CODED IDENTIFICATION MEMBER FOR USE IN AN AUTOMATIC OBJECTIDENTIFYING SYSTEM COMPRISING A SCANNING STATION INCLUDING A SOURCE OFRADIANT ENERGY SIGNALS OF GIVEN WAVELENGTH, RADIATING MEANS FORRADIATING SAID SIGNALS WITH A FIRST PREDETERMINED POLARIZATION, ANDRECEIVING MEANS FOR RECEIVING RADIANT ENERGY SIGNALS OF SAID GIVENWAVELENGTH BUT LIMITED TO RECEPTION OF SIGNALS HAVING A SECOND ANDSUBSTANTIALLY DIFFERENT POLARIZATION, SAID IDENTIFICATION MEMBERCOMPRISING: A PLURALITY OF INDIVIDUAL REFLECTOR ELEMENTS ARRANGED IN APREDETERMINED CODE SEQUENCE, EACH EFFECTIVE TO REFLECT IMPINGING RADIANTENERGY SIGNALS OF SAID GIVEN WAVELENGTH BUT WITH SAID SECONDPOLARIZATION; AND MEANS FOR MOUNTING SAID REFLECTOR ELEMENTS ON ANOBJECT TO BE IDENTIFIED IN POSITION TO INTERCEPT AND RE-RADIATE SAIDRADIANT ENERGY SIGNALS FROM SAID RADIATING MEANS BACK TO SAID RECEIVINGMEANS WHEN SAID OBJECT IS IN PREDETERMINED POSITION RELATIVE TO SAIDSCANNING STATION.